This invention relates to display devices, and particularly to ferroelectric liquid crystal display devices.
The majority of liquid crystal displays (LCDs) rely on the use of two polarisers to render visible the difference between the switched and unswitched regions. These polarisers are disposed one each side of the LC cell. The appearance of the display depends critically on both the performance and the alignment of these polarisers.
For example, in a twisted nematic LCD, one polariser is aligned so that its absorption axis is either parallel or perpendicular to the alignment direction of the liquid crystal molecules (the director) on the neighbouring wall of the cell. The other polariser is arranged either parallel (for a dark OFF state) or perpendicular (for a bright OFF state) to the first polariser, and is placed on the second wall of the cell. Such arrangements are well known in the art.
In ferroelectric LCDs, which operate by switching the LC director in the plane of the LC layer, the polarisers are generally set to be crossed, with one polariser axis parallel to the LC director in one of the display states. Such polariser alignments provide displays with high contrast which are suitable for viewing in transmission and are well known to those skilled in the art.
Reflective LCDs are constructed in the same way, but with an additional reflective layer (generally non-specular) disposed behind the rear polariser. Therefore light passes through the polariser/LC cell/polariser combination twice in opposite directions. It is found that displays constructed using conventional methods described above are very dull and difficult to read. They maintain high contrast, but, because of the double passage of the light through the display, the nominally "bright" states are, in fact, also rather dark, making them difficult to use.